According to a spokesperson for the ICO, it is too early to say which part of the data protection law Facebook may have infringed by conducting its experiment.

The ICO can conduct independent investigations on individuals or organisations that are involved in data or privacy law breaches, and the regulator can also impose fines ranging up to £500,000, reports Reuters.

Companies found guilty during the probe would also need to change their data protection and privacy policies.

Apparently, Facebook's secret study did not result in a breach of its terms of usage and service, even though users were not given prior notifications about the company's experiment.

Emotional Contagion study

According to Facebook, the primary reason behind the study was to assess how users responded to emotional posts and content. The company says it was imperative to determine how users reacted to both positive and negative news feed content.

During the test period (11-18 January 2012), actual user Facebook posts were not altered visibly. Apparently, posts could be viewed intact from a friend's Facebook profile.

"We are sorry"

Adam Kramer, engineer behind the controversial emotional contagion study, has tendered a public apology to users, stating that the company's 2012 experiment was a result of the social networking site's "growing concern" towards its users.

"We felt that it was important to investigate the common worry that seeing friends post positive content leads to people feeling negative or left out," said Kramer.

However, another surprising revelation by Kramer reflects on Facebook's apprehensions about users deserting the site after being exposed to friend's news feeds having negative content.

"we were concerned that exposure to friends' negativity might lead people to avoid visiting Facebook. We didn't clearly state our motivations in the paper," Kramer revealed.

Facebook's user desertion concerns were not stated earlier.

"Having written and designed this experiment myself, I can tell you that our goal was never to upset anyone. I can understand why some people have concerns about it, and my co-authors and I are very sorry for the way the paper described the research and any anxiety it caused," Kramer concludes.

Facebook's 'emotional contagion' study was first made public by the Proceedings of the National Academy of Science (PNAS) journal.